Renaming CPPM should do it, but if you can't for some reason you can copy the print template that is being used for the confirmation email to have the full URL of your choice as well.
You can copy the template under Configuration --> Print Templates; make your changes; and then reference this new Print Template within the self-registration page configuration.
For example:
A visitor has requested access naming you as the sponsor. Please <a href="{'https://<Name or IP of your choice>/guest/guest_register_confirm.php'|NwaGetAppUrl:false:$u.require_auth}?{if $u.source}gsr_id={$u.source|rawurlencode}&{/if}token={$u.register_token|rawurlencode}" target="_blank">click here</a> to confirm or reject the request.
{else}
A visitor has requested access naming you as the sponsor.
Do you <a href="{'https://<Name or IP of your choice>/guest/guest_register_confirm.php'|NwaGetAppUrl:false:$u.require_auth}?{if $u.source}gsr_id={$u.source|rawurlencode}&{/if}token={$u.register_token|rawurlencode}&confirm=1" target="_blank">confirm</a>
or <a href="{'https://<Name or IP of your choice>/guest/guest_register_confirm.php'|NwaGetAppUrl:false:$u.require_auth}?{if $u.source}gsr_id={$u.source|rawurlencode}&{/if}token={$u.register_token|rawurlencode}&confirm=0" target="_blank">reject</a> the request.